X-ray grid actuating device



Oct. 16, 1956 R. J. STAYA EI'AL X-RAY GRID ACTUATING DEVICE 3 Sheets-Sheet 2 Filed July 21 1951 F. HQMAW.

r 2,767,323 Patented Oct. 16, was

X-RAY GRID ACTUATING DEVICE Robert J. Stava, University Heights, Walter G. Reininger,

Cleveland, and David M. Barrett, Lyudhurst, Ohio, assignors to Picker X-Ray Corporation, Waite Manufactuging Division, Inc., Cleveland, Ohio, a corporation of i0 Application July 21, 1951, Serial No. 237,898

7 Claims. (Cl. 25062) This invention relates to X-ray radiography and is particularly concerned with means for eflfecting controlled reciprocation of the grid, which is employed to reduce fogging of the film by secondary radiation.

One of the objects of the invention is to provide simple and eifective mechanism self-contained on the exterior of the frame surrounding the bucky and operating to reciprocate the bucky within the frame.

Another object is to provide an automatically actuated switch control for the X-ray device to prevent exposures at or immediately adjacent the points of reversal of movement of the grid which would tend to cause an image of the grid on the film. We have provided readily adjustable means, actuated by the grid reciprocating mechanism for determining the portion of the movement of the grid in which the exposure may be made, thereby insuring that exposure may always be made at a desired distance from the points of reversal of the movement.

A further object is to maintain a grid velocity which is independent of friction changes in the mechanism, of voltage fluctuations of the driving motor, and of frequency changes in the source of alternating current supply. The foregoing are important, particularly in the operation of mobile X-ray units which are apt to have wide frequency variations as a result of generating the source of electric energy from either gas or diesel operated motor generators. In other words, it is important that the motor be sensitive to frequency changes in order that the speed of the grid may be adjusted to the output of the X-ray tube.

The reciprocating mechanism itself and the electric control will be more apparent from a detailed description of a preferred embodiment illustrated in the drawings hereof, which will follow after a summary of the difierent news.

The foregoing objects are carried out in the preferred manner by mounting an electric motor on one side of the bucky frame and operatively connecting the motor through a cam mechanism to the grid which is mounted for reciprocation within the frame. The cam is so designed as to give uniform acceleration and deceleration to the grid, with equal intervals of time for the travel in each direction. Moreover, the motor utilized is of the synchronous type which is driven by the same source of alternating current supply as the X-ray tube, whereby the grid speed accurately follows the longer or shorter intervals of X-ray exposure flashes from the tube notwithstanding frequency variations in the source of current supply.

In the drawings, Fig. 1 is a perspective of an X-ray exposure table provided with a longitudinally adjustable frame surrounding a grid which may be reciprocated by our mechanism, the casing enclosing the reciprocating mechanism being indicated in this view in dotted lines; Fig. 2 is a vertical section on a larger scale than Fig. 1 extending from front to back of the table in the general regionindicated by the line 2-2 on Fig. 1 and showing the grid with the cassette beneath it; Fig. 3 is a perspective partly broken away of the shiftable frame carrying the grid and cassette, the latter being mounted on the laterally movable tray; Fig. 4 is a detail of the grid support in the location indicated by the line 44 on Fig. 3; Fig. 5 is a plan of the shiftable frame with the top plate removed and showing also the grid partly broken away and the reciprocating'mechanisrn carried by the exterior of the frame for operating the grid, the top plate of the casing which encloses the reciprocating mechanism being also removed; Fig. 6 is a sectional elevation on a larger scale of the reciprocating mechanism, the view being taken in a plane indicated by the line 6-6 on Fig. 5; Fig. 7 is a detail of the gearing of the reciprocating apparatus, being a.horizontal section in a plane indicated by the line 7 7 in Fig. 6; Fig. 8 is a diagram illustrating the nature of the periodic reciprocations of the grid; Fig. 9 is a plan of the reciprocating mechanism shown in Figs. 5, 6 and 7, on a larger scale and with the parts turned in the opposite direction and with the addition of the automatic switch controls for the X-ray machine; Fig. 10 is an elevation of the mechanism of Fig. 9, sectioned through the motor shaft as indicated by the offset line 10-10 on Fig. 9; Fig. 11 is a detail of the switch operating mechanism, being a vertical section on the line 11'11 on Fig. 9; Fig. 12 is a diagram illustrating the operation of the switches controlling the period of exposure with reference to the reciprocation of the grid.

Fig. 1 of the drawings illustrates conventionally an X- ray table having an X-ray transparent top 10, vertical front and rear walls 11 and a suitable supporting base 12. Above the table we have indicated an X-ray tube X directing its rays x downwardly onto the top of the table. In the front wall of the table 11, shown in Fig.

l, is a longitudinal slot 15 through which the cassette is' inserted into a longitudinally shiftable frame carrying the grid, as about to be explained.

Carried by the front and rear Walls 11 of the table are supporting ledges 16 and 17, Fig. 2, which carry the longitudinally slidable frame 20. This frame has a boundary member formed with a vertical rear wall 21, and side walls 14 and 18, and a front rail 19. The rear and side walls have inwardly directed flanges 22 and 23 at the upper and lower edges thereof,'while the rear wall and front rail have downwardly and outwardly extend ing members 24 carried thereby. These members 24 hook under the ledges 16 and 17 of the table While the front rail and the flange 23 on the rear wall rest on top of those ledges. The frame is accordingly permanently mounted in the table but is shiftable longitudinally there in. At its top the frame is covered by a flat plate 25.

Resting on the upper surfaces of the bottom flanges 23 of the frame 20 is a horizontal plate or tray 3% having a downwardly extending front lip 31 forming a finger grip by which it may be drawn out through the table slot 15 irrespective of the position of the frame in the table. The tray 30 is adapted to carry the cassette 35 and has means for holding it in place on the tray. The means shown comprise the clips 36 secured to the tray and overhanging the top of the cassette. The cassette may accordingly be readily slid into place between these guiding members 36 when the tray has been pulled out at the front of the table.

Above the tray 30 and the cassette carried thereby the frame movably supports the grid 40. The grid has a surrounding frame 41 with inwardly overhanging top and bottom flanges binding in place the material of the grid. If desired, the grid may have X-ray transparent top and bottom plates, as illustrated by the top plate 40a in Fig. 5.

As shown particularly in Figs. 4 and 5 the forward edge of the grid is supported by a pair of rollers 42 carried thereby and tracking between the top flange 22 and an intermediate inwardly extending flange 26 on the side one switch controlling both. 7 g V 1 On the other hand, with high-powered X-ray apparatus, 7 where the exposure is of the order of V of "a second,

' wall i The rearward edge" of the grid carries'a pair of brackets 43 which extend outwardly through slots in the:.,

7 side wall 14' of the frame 20 and rest slidably on a pair of rods 45 and 46 mounted in channel-shaped brackets he 28 andt29 secured to the outer side of the/rear. wall 21 of the frame 20. a

n will'be seen from Fig. that the grid while having a width only slightly less than theinterior ofthe frame is maten'ally'shorter than the open space in the length of the frame, and accordingly the grid may be shifted back and forth longitudinally within such open spaceQ The means for'so shifting the grid is carried by the frame itself on its exterior and will now be described with references to Figs. 5, 6 and 7-, and also Figs. 9;and'10.

' Asshown in the 'views above meritioned, we have pro-a vided a longitudinal bar 50 secured at one end to a downtherotation of which reciprocates the gIidwithin the frame.

JInthe construction shown in Figs. 16-and 7 we have provided: a vertical plate 53 rigidly mounted on the frame 20 in position spaced outwardly therefrom and V parallel therewith, the mounting being, for instance, by

corner pins 49, one ,of' which is illustrated in 'Fig. 5'. Journaled in the wall 14of the frame and in 'the plate 53 .is a shaft 54 carrying the heart-shaped cam mentioned. The shaft extends outwardly beyond the cam,

passes through a slot 55 in the bar 50 and forms a guide therefor, as shown in 'Fig. 6. a V T0. rotate the shaft 54 and hence the heart-shaped cam We have indicated such motor at 60, as being mounted on a plate 61 (Fig. 6) extending fromtheframeltl.

Themotor is shown'as having-a pinion 62 meshing with a gear 63 on a shaft 64 journaled'in the Wall 14 and plate 53. This shaft carries also a pinion 65 which meshes with the gear 66 on a lay shaft67 also journale d in the frame and plate 53. The shaft '67 carries a pinion 68 which meshes with a gear 69 on t-he'cam shaft 54;

The. above description'applies also to Figs. 9 and 10, except that in those figures the'plate 53 is omitted and the gears are journaled :on studs projecting from the wall .14. V a i It results from the construction described that when the motor is energized thegearing' rotates 1 the heart shaped cam at a reduced-speed and such movement acting on the rollers carried by the 'barl59 reciprocates the grid within the frame 20. 7

. The entire reciprocating mechanism above-described, including the motor, gearing, cam, reciprocating bar and shadow patternsof the'lead strips in the grid. are likely to occur on the film if any of the exposure takes place while the grid:is momentarily stationary, as at a re- 7 To meet that situation," and insure' the exposure coming at another time than versal point in its movement.

one in which the movement 'of the grid is being reversedjwe have provided for automatically controlling the time of. exposure with reference to the position of the grid; The mechanism for accomplishing this and its manner of operation are illustrated in Figs. 9 to 12 which will now be described; I i

j In Figs. 9, 10 and 11, we have illustrated an amplification of our reciprocating :mechanism to effect control of electric switches according to the position of the heart-shaped cam. The mechanism from the motor'to' V the heart-shaped cam issubstantially the same as shown 'wardly. extending portion of the grid .bracketf43 and carrying on 'its'inner face a pair'of spaced rollers 51 t between which operatesa rotary heart-shaped. cam '52,,

'to cause the reciprocation, we. provide asuitable motor and gearing all carried by the wall 1 4. of the frame 20.

in Figs. 5, 6 and 7 and heretofore'de scribed, but in addition thereto we now mount on the shaft 54 of theheartshaped earn a pair of .adjustably positioned cams-8 t} and 99, which respectively control thestarting of'the' movement of the grid and the closing of the X-ray exposurecircuit. These cams are set with reference to the heart-shaped cam so that they will be active at regions other than the extreme end of the stroke, caused by'the point and valley of the heart-shaped cam Thus the starting cam necessarily becomes active when the'grid is in some other region than at a reversal point and the exposure cam becomes active suitably thereafter.

The cam 80 has a hub 81 on one side thereof secured to the shaft 54 by a set screw 82; the earn 9% is shown as having a hub 91 extending in each direction therefrom and'embracing the shaft and secured by' a set. screw 92;

This construction enables each of the cams to be adjusted angularly independently of the other and secured;

for. use tightly on the shaft 540i theheart-shaped cam.

The different positionsfof the active lobes of the two cams 8t and 90 provided by this adjustable mounting is illustrated-for instance in Fig..ll.

Eachlof the cams 80 and 90 is cylindrical for the most" part buthas a projecting lobe, designatedSS and 93 re; spectively. These operate a pair of rollers -85 and 95' which are on swinging arms carried in suitable casings 86 and 96 and each controlling an sliding supports for the grid is mounted in .a convenient position on the outer side of the'frame 20 and carried 7 thereby. It is preferably housed within a casing 70 having an outer Wall, top, bottom and .end walls; The casing is removably mounted'as by screws 71 so that access to the motor, gearing, etc.-, may be obtained when-j 1 jthe'reversal points in the movement of the grid have 7 been foundto be immaterial. Accordingly,"no special regions. Hence it is only necessary to have one manual switch for controlling the driving motor 60, and another manual switch for controlling'the X-ray exposures, of

' which closes its armature switch controlling the circuit to -means need be provided for preventing exposure at such Now the closingof' the push button switch 100 com- 7 pletes a circuit through the motor via the lines A,"B, C, V D and E, and the motor thereupon operates to shift .the

electric switch, as shown in Fig. 12 at 87 and '97.

2 In the diagram" in Fig. 12 the lines designated A E represent a source of alternating c'urrent supply. The line B is normally open at the push button switch 109 and in the homing position the switch 87 is held open by the lobe .83 of the homing cam 80. Accordinglyno current can flow through the motor 60.

grid and at'the same time to turn both'cams and 99;

' As soon as the cam 80 has closed the switch 87 then a return path is provided for the current via that switch and independent'of the push button 100. The witch 87 continues closed during the major portion of the rotation of the cam 80, and during this time the grid is being 7 moved by the heart-shaped cam. The continued rotation of the cam shaft soon brings the lobe 93 of the exposure cam into engagement with the switch roller'95, thus a closing the switch 97 and establishing a parallel circuit from the line'A to B, through the relay R, controlling the X-ray exposure, through the line G, line H, line D, and through switch 87' to line E. This energizes the relay,

the X-ray tube. It also brings into circuit a substitute return lineI shunting around the switch 97, and main:

taining the relay circuit.

Ttresults from the switch controls of the cams, as above explained, that the X-ray circuit is closed for the ex.-

posure at a time after the grid has left one reversal point. The exposed period is'very short-only. a' small fraction of a secondand is accordingly terminated ,bya time i 'switch (not shown) associated with the X-raytube long before the grid reaches its other reversal point. Accordingly, the grid is necessarily moving while the radiograph is being taken, and hence the troublesome grid pattern is avoided.

Where the exposure is for a period of time longer than would be required for one revolution of cam 80, then the switch 100 is maintained in closed position manually, since otherwise switch 87 would be opened, upon the return of the lobe 83 to the position shown in Fig. 12. However, by maintaining the switch 100 closed, the motor 60 remains in operation. The operator maintains the switch 100 closed until after the timer has terminated the exposurethis being made known by an audible sound upon opening of the timer contactors-whereupon the switch 100 is released and the operation of the motor 60 continues until the cam 80 has rotated to the point where the lobe 83 opens the switch 87. A suitable brake (not shown) on the motor stops the rotation thereof while the lobe 83 is still in position to maintain the switch 87 open, wherefore the grid will always stop in the homing position.

If it be desired to operate the grid with random starting rather than the selective system above described, this may be effected by supplying voltage to the circuit through the motor by the lines A and J, controlled by a suitable switch 101. When this switch is closed the motor is energized, and sometime thereafter the operator closes another switch energizing the exposure circuit.

We have found that satisfactory results may be obtained if the speed of the cam is suflicient to shift the grid a distance of 10 lead-lines in 13 cycles, where the motor is operated on 60 cycle A. C. current with half-wave rectification. This would make each 13th lead-line image superimposed upon the first and would be suitable where the lead strips in the grid are approximately .002 inch thick, with 50 of such strips per inch in the grid. Under such conditions, the speed of the grid would be:

Assuming a cam throw of then the total motion of the grid for one revolution of the cam would be 1%. Therefore, with a velocity of .923" per second, a 50-line per inch grid operating on 60 cycle A. C. current should have a cam speed equal to:

=31 65 revolutions per minute =.923" per second .020X l X 60 13 Or, if the grid is moved a distance of inch (distance between the centers of two adjacent strips) during 13 cycles, the speed of the grid would be:

%3235 inch per second Thus, for any time interval equivalent to 13 cycles, non-synchronous operation of the grid can be obtained by moving it a distance of 3 inch; inch; inch, etc., up to inch.

On the other hand if a time interval of twelve cycles is utilized, then non-synchronous speeds could be obtained by moving the grid during 12 cycles, inch; 3 inch; A-, inch, etc-utilizing prime numbers of 12. In any =.0923 inch per second 6 t event, the number of cycles betwee'n'a repetition (superimposure) of the grid lines, is dependent upon the shortest exposure time for which the bucky will be used. Such number shall not exceed the number of cycles of the exposure, but it should be keptas high as possible, for' the reason that'a short movement of the grid during exposure shows all irregularities in the strip spacing on the film in the form of lighter or darker clouds, whereas higher velocities stretch the clouds out and make them fade on the film.

From the foregoing, it is apparent that there is a critical relationship-between the frequency of the current used in the X-ray tube output and the frequency at which the current is supplied to the motor 60. Accordingly, we utilize a synchronous motor and operated by the same source of alternating current supply as that supplied to the X-ray tube] Thus, the grid speed accurately follows all variations in intervals of the X-ray exposures due to frequency changes. As stated aforesaid this is important in mobile X-ray units which generate their source of power from gas or diesel operated motor generators which usually have wide frequency variations. I

It will be understood from the above description and the disclosures of the drawings that we have provided a simple reciprocating mechanism self-contained in an idle space on the outer side of the shiftable frame carrying the grid. The grid may accordingly occupy substantially the full width of the frame and the frame may be shifted as desiredwithout disturbing the connections to the grid actuator, its motor receiving its current by a suitable flexible cable enabling such shifting. The removal of the casing about the motor and gean'ng, readilyeffected when the top of the exposure table is removed, enables convenient access to the motor and gearing.

In its simplest form, our apparatus may be operated merely by a switch controlling the circuit to the grid shifting motor and another switch controlling the exposure. It needs only the addition of the two switch operating cams on the shaft of the heart-shaped cam and the switches and circuits operated by such cams to provide for the automatic control to prevent exposure when the grid is at a reversal point.

We claim:

1. In a device of the character described, the combination of an open rectangular frame, a rectangular grid within the frame having its opposite sides close to the opposite sides of the frame, rollers supporting one side of the grid within the frame, a pair of outwardly projecting arms on the other side of the grid, said alms extending through openings in the adjacent side of the frame to the exterior thereof, a pair of spaced brackets on the exterior of the frame, rods carried by said brackets, said arms having a sliding supporting engagement on said rods, a motor gearing driven thereby and a rotary heart-shaped cam rotated by the gearing, all mounted on the exterior of the frame between said brackets, and a shiftable bar having a pair of spaced rollers engaging the exterior of the heartshaped cam and connected to one of said arms of the grid.

2. In a device of the character described, the combination of a grid mounted for reciprocation, a motor and mechanism operated thereby for reciprocating the grid, cam mechanism operated by said reciprocating mecha nism, a switch actuated by said cam mechanism for determining the starting and stopping of the movement of the grid, an X-ray tube, a second switch actuated by said cam mechanism for determining the initiation of the exposure of the X-ray tube, and means responsive to actuation of the second switch for maintaining the condition established thereby until the first switch is actuated by the cam mechanism to stop the grid movement.

3. In a device of the character described, the combination of a movably mounted grid, a motor, a heart-shaped cam rotatable thereby, a member reciprocated by the cam and connected with the grid for conveying movement to the grid, apair of cams rotatable with the heart shaped cam and adjustable with reference thereto and inde 'pendently of eaehzother, a pair of electric switches Q0111? trolled by said adjustable cams, one of said switches coacting with one cam .10 startand stop the grid movement and the other switch eoacting withthe other cam to conditiontthe Xaaytribel for exposure, and means'responsive toaetuatio'n of the latter switch for maintaining the condition established thereby until the first switch is'aetuated by the cam mechanism to stop the grid movement.

4.. The combination of an X-ray table, a frame shiftably mounted therein, a movably mounted grid in the a frame, reciprocating J mechanism therefor including a motor, gearing driven thereby, .a heart-shaped cam'rotated' by the gearing'and reciprocating member operated by the heart-shaped cam, all of said mechanism being mounted on the frame, afconneetion between the reciprocating memher and thegrid, a pair of independently adjustable cams operated ,by said mechanism, a pair of' rotary grid mounted for reciprocation with respect to the tube, V

a synchronous motor in circuit with said source of alternating current supply for the tube, whereby a current of identical frequeney'fiows through the motor and tube circuits, "said grid having stripsof material opaque to X- rays and spaced at regular intervals therein, and means connecting the motor to the grid so as to move the grid during tube exposure at a speed which will avoid synchronism of the grid strips with ,anytrequency er, current used for operating said tube I ,7

6.111 X ray apparatus,;,the combination of an,.X ray tube, a source of alternatingcurrent supply, for theoutput thereof, a grid mounted for movement with respect ,to, the

tube, a synchronous mntor in circuit with saidsourceof' alternating current supply, means opera-tively connecting the motor to the grid for reciprocating it during tube exj-' I posure in timed non-synchronous relationship with respect to the frequency of the current supplied to said tube, said means including gearing'driven by said moton; anda rotary heart-s'haped cam rotated by the gearing-andengaging the grid for reciprocation atthe same speed "in each direetion. I a i 7. in an X Iay apparatugthe combination of an X-ray tube, a source of alternating current supply for the. output of the tube, a grid mounted to'r movement Withrespect'to,

the tube, asynchronous motor in eirciuit with saidsource of alternating icurrent'supply, mechailism driven by, said synchronous motor for reciprocating the grid during tu be ez posureand at a speed that is non synehronous withrespect to the frequency of the current supply, said meohaa nism including means for maintaining the' speed oft-he grid the same in each direction; 7

References Cited in the file or this patent 'f V UNITED STATES PATENTS 1,471,081 Waite Oct, 16,1923

2,132,774 Brown' a Oct '11, 1938 2,204,347 Files June 11,1940 2,205,209 "Kunz eta]; June 18, 1940 2,208,265 Kiz'aur July 16, 1940 2,504,864 Morgan et a1. Apr. 18, 1950 7 2,534,623 Pitts et a1. Dec. 19, 1950 2,591,536 Gieringer et al Apr. 1, 1952 

